SQLQuery problems - error: "function does not exist"

I'm using SQL2008 AS and DB, downloaded and registered the correct DLL on my SSAS instance and am able to use certain functions like GetDefaultDrillthroughMDX and GetCustomDrillthroughMDX
without issue (both of them ran well in a rowset action expression).

However I really
need to access the database in my rowset action drilldown (long, boring story) and need to use the SQLQuery.ExecuteSql method. Here's my syntax for the action expression:

Sorry for the slow reply. Note in the ASSP project, the SQLQuery assembly is a separate assembly. Note it's a separate download in the Downloads tab. This was done purposefully so that you could make sure to set permissions appropriately. (Be 100% sure not
to run the assembly as the service account or else a smart user could drop a database easily. And make sure not to use SQL security as a smart user will be able to see the password.)

Then I Imported The DLL in SSAS solution
And in SSAS Action Expression I used the following
"Call ASSP.SQLQuery.ExecuteSQL('Provider=SQLNCLI;server=LocalHost;database=SD;trusted_connection=yes','exec [dbo].StoredProcedure');"

Then I Deployed My Cube solution
And in the Analysis Server , I set the Assembly properties to Impersonation=Default and Permission Set=Unrestricted

Then I go to excel 2010 and right Click on my data Then Click on Additional Actions , I get An Error
Query (1,6) The '[ASSP].[SQLQuery].[ExecuteSQL]' Function Does not Exist.